I. Field
The following description relates generally to communication systems, and more particularly to uplink SDMA pilot estimation.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communication systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input or Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for the next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
Spatial Division Multiple Access (SDMA) is a multiple access scheme which enables multiple streams transmitted to different receivers at the same time to share the same frequency channel and, as a result, provide higher user capacity. SDMA is a common and typical MIMO scheme in cellular wireless systems. In an uplink SDMA transmission, each spatial stream may exhibit a different common phase error because of frequency errors and phase noise differences between different uplink users (access terminals). A number of methods are employed to estimate common phase errors for each user in an uplink SDMA transmission.